On Mon, 03 Oct 2005 00:13:54 -0400, TRABEM wrote:
On Mon, 03 Oct 2005 01:09:33 GMT, wrote:
I put your tirade on the end of this as it's not relevant to the
orininal question.
The original post (by A*s*i*m*o*v) mentioned back to back diodes as
protection, so my reply was quite relevant.
If it was about overload yes. It was about bandwidth and noise.
Not sure what ruffled your feathers so badly Allison. But, whatever it
was, I am sorry if I did something that didn't meet with your
approval.
You really came in with and attitude. but completely missed the real
subject of the question.
I also worked professionally as an avionics tech, and was in the
business when the first Motorola commercial repeaters using
synthesizers were put up...and they wondered why the other repeaters
on the same tower couldn't hear well. That only took 'em about 10
years to figure out. Then, about 10 years after that, they started
using gasfets, and it took them another 10 years to figure out they
didn't do well in high rf fields. By then, it was the 1980's.....but
at least they got it right eventually.
We are talking presynth. I had my First Class before that.
My first commercial UHF repeater was built from U44 components then
later Motrac as they were current radios For 1971-2 that was pretty
good. The motrac front ends were 6 cavitys a mixer then IF
selectivity, crunchproof. LO was always a crystal for least phase
noise. Anyone that read papers by Rhode understood this in the
early to mid 70s.
Maybe you designed some of those early nightmarish radios yourself?
I take that as insult.
Gads no, I thought they were crap too.
I'm not all that thrilled with the ARC308C or worse 324 and the put
them in planes. I know that as I have a 308 as backup. Gag, Ick,
ick. but at 1500 to 2k for a new one I'll keep it till it quits.
Anyway, I wish you luck. And hope you realize the importance of
keeping the front end clean, which sometimes means dumping the gasfet
and using a bipolar preamp instead.
Your being pendantic again.
I'm not big on gasfets untill I get above 1GHz. At 6m a u310 bipolar
fet in common base gets me about 12db. With a good IP and noise
figure. Just enough to get past the image stripping filter before the
Level-7 DBM. That makes for a nice crunchproof frontend that with
sub 3db noise figure. If I could get that noise figure without the
fet I'd not use it but I need the gain. I've tried mrf571 in a norton
push pull configuration, hard to overload but the 100ma standing
current was hard to take for portable ops!
If your interested, ops here are QRP weak signal 6m SSB and 2M ssb
and occasionally CW using solar power and battery. Power consumption
is a consideration as well as perfomance. Overload performance with
a KW 800ft away and in band is well challenging. The challenge is to
get enough gain to ovecome the mixer noise without having a watt of
power at the mixer.
Actually, I hope the original poster (A*s*i*m*o*v) got the message
about introducing gross non linear back to back diodes across the
antenna terminals.
That is true. However think about it for more than a second. Diodes
or not hes talking about gain, bandwidth and noise so even without
the diodes hes already running wide and risking overload at the next
stage. Without selectivity you get cascade overload. The classic
problem of weak reciever fix of stacking gain before it and watching
the input overload threshold wander in to the -40dbm (or worse)
region. Bad way to fix the problem.
Allison
KB1GMX